1. Field of the Invention
The invention relates to a bimetal thermometer. The invention especially relates to a bimetal thermometer comprising a cup-shaped casing which has a bottom wall and supports a window at its edge opposed to the bottom wall, a casing carrier to which the bottom wall is attached, a protective tube having a free closed end and being connected to the casing carrier at its other end, and a bimetal helix arranged inside the protective tube and being attached with its first end to the free end of the protective tube. A dial and a pointer which is fixed to a pointer shaft are arranged inside the casing. The pointer shaft is rotatably journaled by means of a bearing assembly, extends through the casing carrier and is connected to the second end of the bimetal helix such that a temperature-dependent rotation of the second end of the bimetal helix causes a rotation of the pointer shaft.
2. Related Background Art
A bimetal thermometer comprising the aforementioned features is known. In order to measure the temperature of a measuring substance at a measuring point by means of the bimetal thermometer the latter is mounted at the measuring point such that the protective tube is surrounded by the measuring substance so that the protective tube and the bimetal helix arranged inside the protective tube take the temperature of the measuring substance. In the case of a change in temperature the second end of the bimetal helix performs a rotation about the axis of the bimetal helix. This rotation is transmitted to the pointer via the pointer shaft so that the pointer takes a position in front of the scale of the dial corresponding to the prevailing temperature and thereby the value of the temperature is indicated on the scale.
When during operation vibrations which cause a vibration movement of the pointer are transmitted to the bimetal thermometer, this impedes reading of the temperature value from the scale. Furthermore vibration movements of the movable members of the bimetal thermometer increase the wear thereof. In order to prevent these drawbacks it is known to fill the bimetal thermometer with a damping liquid so as to damp the vibration movements by liquid friction. The damping liquid which may be, for instance, silicone oil is provided either both in the casing and in the protective tube or only in the protective tube. As the temperature stability of the damping liquid is limited, the indicating and measuring range of bimetal thermometers damped by a damping liquid has an upper limit. Such bimetal thermometers cannot be used for temperatures of more than 160° C., for instance. It is furthermore a drawback that the measuring substance is rendered impure by the damping liquid, if the bimetal thermometer gets leaky and the damping liquid escapes.